Valve has made some key changes to Steam's gifting system in an effort to standardize the feature, a move that hurts key resellers like G2A...but also harms overseas gamers.
The major change to Steam's gifting system is that gamers can no longer gift a game to users in other countries if there's a huge price difference between the two regions. For example, games are typically cheaper in the U.S. than in Australia, so many overseas gamers ask their U.S. friends to buy a game at a cheaper price and gift it to them and remunerate the buyer via Paypal. That option is no longer available if the games have a price difference of 10% or more across regions.
This move specifically harms key resellers in two ways. Resellers typically buy tons of games from overseas regions at a discounted rate via sales, and then sell them in other countries for profit via gift codes. Valve no longer allows gifting via email, so you can't send a gift Steam game code to someone via email. Plus Steam now restricts overseas purchases in the aforementioned way.